1. Field of the Invention
The present invention relates to a coupler-containing photographic silver halide emulsion and a method for the formation of color photographic images using a coupler and, more particularly, to a photographic silver halide emulsion containing a novel yellow color-forming coupler and to a method for the formation of color photographic images.
2. Description of the Prior Art
In the formation of color images in subtractive color photography, an aromatic primary amine compound, especially an N,N-disubstituted p-phenylenediamine compound, is used as a developing agent, to reduce the silver halide grains in an exposed photographic silver halide emulsion, and the concurrently produced oxidation product of the developing agent reacts with the coupler to form a cyan, magenta or yellow dye image.
The couplers used in the above-described color photographic process have a phenolic hydroxy group, an anilinic amino group or an active methylene group, and, by oxidative coupling with the aromatic primary amine developing agent, form dyes which absorb light in the visible wavelength range.
Yellow dye images show a specific absorption to blue light in wavelengths ranging from about 400 to 500 millimicrons. Previously known yellow-forming color couplers include .beta.-ketoacetoacetic acid esters, .beta.-diketones, N,N-malonic diamides and .alpha.-acylacetamides, of which the .alpha.-acylacetamides have been widely used as advantageous yellow color-forming couplers in the field of color photography.
The .alpha.-acylacetamides as couplers and the yellow dyes derived therefrom as images have, however, a number of disadvantages and are by no means completely satisfactory. For example, conversion of the .alpha.-acylacetamides to the azomethine dyes require 4 equivalents of silver halide as the oxidizing agent, per molecule, and, moreover, the maximum molecular extinction coefficient of the dyes formed is only on the order of about 20,000 liter/mol.multidot.cm.
Many investigations have been made in order to improve these disadvantages. For example, .alpha.-acylacetanilides wherein one of the hydrogen atoms of the active methylene group is replaced by a halogen atom, such as fluorine or chlorine, a sulfoxy group, an acyloxy group, etc., as described in U.S. Pat. Nos. 3,369,895, 3,408,194, 3,415,652 and 3,447,928 were developed for the purpose of reducing the amount of silver halide necessary in a light-sensitive material and improving the coupling reactivity. However, these couplers have the disadvantages that the coupling reactivity is still insufficient, a marked color fog is produced, the couplers per se are unstable or the fastness of the color images formed therefrom is insufficient.
As the result of further investigations to overcome these disadvantages, couplers in which one of the hydrogen atoms of the active methylene group is replaced with an imido group as described in British Pat. No. 1,386,151, and the couplers as described in U.S. Pat. No. 3,894,875, have been developed. However, these couplers are also still insufficient from the standpoint of coupling reactivity and the fastness of the dye images formed. Furthermore, couplers capable of being used to produce images of high quality, such as sharpness, graininess, etc., and also having a high coupling reactivity are required, in particular, in light-sensitive materials having high speed, such as color negative or color reversal light-sensitive materials for taking photos. However, these properties of the above-described couplers are also insufficient.
Still further, the couplers described in German Patent Application (OLS) No. 2,556,620 are still insufficient from the standpoint of coupling reactivity and properties for providing images of excellent image quality, such as sharpness, graininess, etc.